The present invention relates to a parameter correction circuit and a parameter correction method which correct production deviations in parameters of a device such as a resistor element, and are desirably applied to a PLL (Phase Locked Loop) circuit to be included in a semiconductor integrated circuit for use in, for example, a data writing/reading system of a recording-type optical disk.
Conventionally, in a recording-type optical disk, for example, a DVD-R and a DVD-RAM, address signals, referred to as wobble signals, are physically located in its tracks. A PLL circuit, which is included in a semiconductor integrated circuit for use in a data writing/reading system of such a recording-type optical disk, multiplies the wobble signal 186 times to generate a recording clock so that based upon this recording clock, data is written on an recording-type optical disk in an unrecorded state.
Here, as shown in FIG. 10, such a PLL circuit is provided with a phase comparator 50, a charge pump circuit 51, a filter circuit 52, a voltage control oscillator 53 and a frequency divider 54. With respect to writing process onto the recording-type optical disk, in the case where a plurality of speed modes of the writing process, such as onefold, twofold, fourfold and eightfold speed modes, are prepared, the loop band of the PLL circuit needs to be changed in accordance with this set speed mode. In order to change the loop band, in general, in an open loop characteristic diagram shown in FIG. 11, the loop band needs to be changed, with ratios of a gain cross-point fc, a pole point fpole and a zero point fzero being maintained at constant values. For example, upon changing the speed from the onefold mode to the twofold mode, the above-mentioned gain cross-point fc, the pole point fpole and the zero point fzero need to be respectively doubled.
More specifically, factors that are used for changing the loop band while maintaining the above-mentioned ratios at constant values include the resistance value of a resistor 52r included in the above-mentioned filter circuit 52, a charge pump current outputted from the charge pump circuit 51, a gain of the voltage control oscillator 53 and a frequency-dividing ratio of the frequency divider 54, and these factors need to be changed. With respect to the method for changing the loop band by changing the resistance value of the resistor 52r included in the filter circuit 52, in an attempt to include the resistor 52r inside a semiconductor integrated circuit, since the resistance value of the resistor 52r generated inside the semiconductor integrated circuit also deviates in response to deviations in manufacturing processes of the semiconductor integrated circuit, it becomes difficult to include the resistor 52r therein. For this reason, the resistor 52r is included in the filter circuit 52 as an externally added part, as shown in FIG. 10.
However, in the case where the resistor 52r is included as such an externally added part, a plurality of resistors 52r need to be included depending on writing speed modes, and since the number of terminals to be prepared in a semiconductor integrated circuit is limited, it is difficult to include resistors 52r, the number of which is the same as the number of the speed modes to be set, as externally added parts. Moreover, since various recording-type optical disks, such as DVD-Rs and DVD-RAMs, have different loop bands to be used, the number of the resistors 52r required is represented by the number of speed modes multiplied by the kinds of recording-type optical disks to be applied; thus, in an attempt to use a PLL circuit compatibly in these various recording-type optical disks, it becomes difficult to include the required number of resistors 52r as externally added parts by using the limited number of terminals prepared in the semiconductor integrated circuit.
For this reason, for example, JP-A No. 03-150613 has disclosed a technique in which, a parameter correction circuit for correcting influences from production deviations in a resistor is included in a semiconductor integrated circuit, and a variable resistor is included in the semiconductor integrated circuit so that the resistance value of this variable resistor is changed.